Aluminum alloy cartridge case



Filed Aug. 27, 1958 OXIDE LAYER IE-ZO/MTHICK LA CQU ER LAYERl5-2S/u.THlCK ALUMINUM ALLOY f/VVE/VTDF Wm TEE 50/4/1775? United StatesPatent bfifice Y 3,048,105 Patented Aug. 7, 1962 3,048,105 ALUMENUMALLOY CARTRIDGE CASE Walter Schlatter, Vaduz, Liechtenstein, assignor toPress- & Stanzwerk A.G., Escher], Liechtenstein Filed Aug. 27, 1958,Ser. No. 763,414 Claims priority, application Germany Sept. 2, 1957 4Claims. (Cl. 102-43) The invention relates to aluminum alloy cartridgecases,

and has the primary object of providing such cartridge cases which aresafely protected against erosion by the hot combustion gases developingwhen firing a shot.

It is another object of the invention to provide a cartridge case madeof an aluminum alloy which is safely protected from being partly fusedat its mouth by the hot combustion gases issuing therefrom when firingthe shot whereby the fouling of the gun barrel by such fused metalcondensing on its inner surface is prevented.

It is yet another object of the invention to provide a method for theprotection of aluminum alloy cartridges from erosion and part-fusion bythe hot combustion gases when firing a shot.

It has been proposed to prevent the erosion and partfusion of the mouthof a cartridge case made from aluminum alloy by the hot combustion gasesissuing at high pressure from said mouth when firing the shot byapplying an oxide layer to the surface of the cartridge case by anodicoxidation. In order to give effective protection against the abovephenomenon, called burning-out for brevity, a minimum thickness of thesaid oxide layer of 40a would be required.

However, it has been found that the thickness of the said oxide layercannot be increased to this value required for an absolute protection ofthe case because the deformations which occur at the mouth of the casewhen the projectile is inserted therein, produces a strain whichoverstresses and damages such thick oxide layers. The damaged oxidelayer, crossed by fine cracks, has not proved to afford sufi'icientprotection against the erosive hot combustion gases.

It is yet another object of the present invention to provide a cartridgecase of aluminum alloy which has good sliding properties as required forejecting the spent cartridge case from the weapon.

With these and other objects in view, which will become apparent laterin this specification, I provide an aluminum alloy cartridge casecomprising in combination: an aluminum alloy cartridge case proper, anoxide layer covering said case, and a lacquer layer at least partlycovering the said oxide layer.

According to a preferred embodiment, the said lacquer I layer iscomposed of a synthetic resin layer based on ethoxylene (epoxy) resin.

Owing to its resiliency such a lacquer prevents cracking resulting fromthe deformation which occurs at the mouth of the cartridge case when theprojectile is driven into said mouth and said lacquer also cooperateswith said oxide layer to provide the protection of the metal that isrequired and desired against corrosion as well as against the erosionand burning out of the mouth of the case when firing a shot.

Applying the said lacquer not only to the inner surface but also to theouter surface of the case has proved advantageous in view of its goodsliding properties when ejecting a spent cartridge from the weapon afterfiring a shot.

The drawing illustrates a cartridge case made according to theinvention.

The method I provide according to the present invention comprises thefollowing consecutive steps: producing an oxide layer by anodicoxidation on an aluminum alloy cartridge case, dipping the said anodisedcartridge case into a lacquer bath, removing excess lacquer from thesaid cartridge case by dripping and centrifuging, drying the lacquerremaining on the surface of the said cartridge case by heating to amedium temperature for a moderate period, dipping the said cartridgecase a second time in the said lacquer bath, removing again excesslacquer by dripping and centrifuging, and baking-in the said lacquer onthe said cartridge case for a prolonged period.

Preferably the lacquer is applied at a viscosity determined by the timefor flowing ofi a Ford beaker at room temperature.

In order that the invention may be clearly understood and readilycarried into effect, the same will now be described by way of example.

The cartridge case proper consists for example of an aluminum alloy ofthe kind Al-Zn-Mg-Cu 54. This cartridge case proper is covered by anoxide layer of a thickness of 15 to 20,11.. This oxide layer is coveredby a lacquer layer of a thickness of 15 to 25 The following is anexample of the method according to the present invention:

*On the surface of a cartridge case proper made of an aluminum alloy ofthe kind Al-Zn-Mg-Cu 54, an oxide layer of 15 to 20,1 is produced byanodic oxidation. Densifying of this oxide layer by a known sealingprocess is preferably dispensed with.

The said oxidised cartridge case proper is dipped a first time into alacquer bath, and after removing the excess lacquer, the oxidisedcartridge case is dried for 20 minutes at an oven temperature of C.Subsequently the cartridge case is dipped into the said lacquer bath asecond time, excess lacquer is again removedby dripping andcentrifuging, and the adhering lacquer is baked-in by heating for onehour at an oven temperature of The lacquer is preferably applied at aviscosity defined by the period of 27 to 28 seconds required for flowingout of a Ford beaker No. 4, measured at a room temperature of 20 C.

The lacquer layer produced should preferably have a thickness of 15 to25p.

What I claim as my invention and desire to secure by Letters Patent is:

1. A cartridge case comprising in combination, an aluminum alloy caseproper with a mouth at one end adapted to be closed by a projectile, andmeans for protecting said mouth from the detrimental effects of the hotcombustion gases when firing, said means comprising at anodic oxidelayer having a thickness of about 15 tc about 20 and a layer of resinhaving good sliding properties baked on the surface of said oxide layer,saic layers covering at least the outside of said cartridge case and theinside of said mouth.

2. A method for manufacturing cartridge cases com prising the followingconsecutive steps: providing an alu minum alloy cartridge case,producing by anodic oxida tion an oxide layer on said cartridge case,said OXidt layer having a thickness of about 15, to about 20 dip pingthe oxide coated case into a bath of resin-base( lacquer, removingexcess lacquer and baking the adherim layer thereon.

3. A cartridge case comprising in combination, an alu minum alloy caseproper with a mouth at one end adapter to be closed by a projectile andmeans for protecting sair mouth from the detrimental effects of the hotcombustio1 gases when firing, said means comprising an anodic OXldllayer having a thickness of about 15 to about 20 1, an a layer of epoxyresin having good sliding properties said layers covering at least theoutside of said cartridg case and the inside of said mouth and beingbaked on th surface of said oxide layer.

4. A method for manufacturing cartridge cases comprising the followingconsecutive steps: providing an aluminum alloy cartridge case, producingby anodic oxidation an oxide layer on said cartridge case, said oxidelayer having a thickness of about 15,14 to about 2011., dippingthe oxidecoated case into a bath of lacquer comprising an epoxy resin, removingexcess lacquer and baking the adhering layer thereon.

References Cited in the file of this patent UNITED STATES PATENTS1,862,565 Burke June 14, 1932

1. A CARTRIDGE CASE COMPRISING IN COMBINATION, AN ALUMINUM ALLOY CASEPROPER WITH AMOUTH AT ONE END ADAPTED TO BE CLOSED BY A PROJECTILE, ANDMEAS FOR PROTECTING SAID MOUTH FROM THE DETRIMENTAL EFFECTS OF THE HOTCOMBUSTION GASES WHEN FIRING, SAID MEANS COMPRISING AN ANODIC OXIDELAYER HAVING A THICKNESS OF ABOUT 15U TO ABOUT 20U, AND A LAYER OF RESINHAVING GOOD SLIDING PROPERTIES BAKED ON THE SURFACE OF SAID OXIDE LAYER,SAID LAYERS COVERING AT LEAST THE OUTSIDE OF SAID CARTRIDGE CASE AND THEINSIDE OF SAID MOUTH.